1. Field of the Invention
The invention relates generally to heavy-duty vehicle frames, and in particular to frames for heavy-duty vehicles such as semi-trailers. More particularly, the invention is directed to a frame which includes one or more vertical bracing structures that replace one or more of the transversely-extending cross members of conventional frames, and which minimizes the need for large and/or numerous gussets, braces and the like that are generally associated with such frames. The frame of the invention more securely supports one or more axle/suspension systems suspended from the frame and more efficiently reacts loads imposed on the frame during operation of the vehicle, while reducing the overall weight and cost of the frame.
2. Background Art
Heavy-duty vehicles, such as tractor-trailers or semi-trailers, typically include one or more suspension assemblies that connect the wheel-bearing axles of the vehicle to the frame of the vehicle. Conventional or prior art frame designs were developed before the advent of air suspension systems for trailers. At that time, spring suspension systems were the suspension of choice for trailers. However, the spring suspension system resulted in a relatively rough ride to the cargo and did not equalize in all situations, thus creating the need for a frame design with soft ride characteristics and efficient equalization characteristics. The subsequent development of air suspension systems provided improved ride quality for individual axles of semi-trailers as well as load equalization among multiple axles.
Load equalization is important because the amount of cargo that a trailer may carry is governed by local, state and/or national road and bridge laws, and is dependent on proper load distribution. The basic principle behind most road and bridge laws is to limit the maximum load that a vehicle may carry, as well as limit the maximum load that can be supported by individual axles. Therefore, the use of air suspension systems that can provide greater load equalization among multiple axles is preferred in order to enable the vehicle to carry as much cargo as is legally allowed. In addition, within the trucking industry, reducing the weight of carrier equipment without sacrificing durability directly improves productivity by increasing the available payload that can be transported by the vehicle. Unfortunately, prior art frames equipped with air suspensions have generally added unwanted weight to the trailer, primarily because those frames were originally built to support leaf spring suspensions and adapting them to incorporate air suspensions required additional bracing and support, such as gussets, braces and the like.
Furthermore, vehicles containing more than one non-steerable axle, including semi-trailers, are subject to lateral or side loads. Lateral loads can act through the frame in opposite directions creating significant twisting torsional loads on the frame. Moreover, a frame is also subjected to strong vertical and longitudinal loads. A durable frame design must effectively react all such loads. Conventional prior art frame designs control vertical loads by utilizing rigid, and therefore heavy, main members and cross members. However, such a rigid structure fails to minimize the effect of lateral and longitudinal loads on the frame. As a result, conventional prior art frame designs have attempted to minimize the effect of lateral and longitudinal loads by utilizing a plurality of gussets, braces and the like variously attached to the cross members, to the frame hangers, to the air springs of the axle/suspension system, and/or to the main members. More particularly, these gussets, brackets and the like typically were attached to and extended between the main members, the cross members and the main members, the cross members and the frame hangers, and the air springs and the main members. These gussets, braces and the like, although helpful in aiding the frame in reacting loads imparted on the frame by the axle/suspension system during operation of the vehicle, add unwanted weight to the vehicle which ultimately reduces the amount of cargo that can be carried by the vehicle.
In some heavy-duty vehicles, the suspension assemblies are connected directly to the primary frame of the vehicle. In other heavy-duty vehicles, the primary frame of the vehicle supports a subframe, and the suspension assemblies connect directly to the subframe. For those heavy-duty vehicles that support a subframe, the subframe can be non-movable or movable, the latter being commonly referred to as a slider box, slider subframe, slider undercarriage, or secondary slider frame. For the purpose of convenience and clarity, reference herein will be made to main members, with the understanding that such reference is by way of example, and that the present invention applies to heavy-duty vehicle axle/suspension systems suspended from main members of: primary frames, movable subframes and non-movable subframes.
More specifically, prior art primary frame designs typically utilize a pair of elongated, longitudinally-extending, spaced-apart, parallel I-beam main members, having a plurality of generally C-shaped cross members which extend between and are connected to the main members. A plurality of generally triangular-shaped gussets typically are attached to and extend between the cross members and the main members and between the air springs and the main members. Additional gussets are also attached to the main members in the vicinity of their respective hangers. Each one of a pair of braces having a generally L-shaped cross section extends diagonally between and is attached to its respective frame hanger and the adjacent cross member. An additional pair of braces each having a generally C-shaped cross section extends diagonally between and is attached to the main members. This frame structure, as mentioned above, is heavy and does not efficiently react lateral and longitudinal loads on the frame.
Thus, the need exists for a frame for a heavy-duty vehicle that is stronger, reacts loads more efficiently, is less costly to manufacture, and is lighter than prior art conventional frame designs. These improvements are provided by the heavy-duty vehicle frame of the present invention which provides a frame for semi-trailers having significantly reduced weight than that found in prior art frames yet has improved strength and capability for more efficiently reacting vertical, longitudinal, roll, and lateral loads. In addition, the present invention provides a frame for semi-trailers, which can be more efficiently manufactured than prior art frames.